Important Questions for CBSE Board Exams 2019

Class X Science – Chemistry – Carbon and its Compounds

Question 1: Why are covalent compounds poor conductor of electricity?Answer 1: Covalent compounds are formed due to sharing of electrons between atoms and no charged particle (ions) are formed, hence such compounds are generally bad conductors of electricity.

Question 2: Differentiate between saturated and unsaturated hydrocarbons.Answer 2: Saturated hydrocarbons: A hydrocarbon in which each carbon atom is attached to four other atoms, is known a saturated hydrocarbon. The bonds so formed are single covalent bonds. These hydrocarbons are also called alkanes. Unsaturated Hydrocarbons: Hydrocarbons contains either a carbon-carbon double bond (C = C) or a carbon-carbon triple bond in their molecules are called unsaturated hydrocarbons.

Question 3: What is catenation? What is its property?Answer 3: The unique property of carbon to form bonds with other carbon atoms giving rise to large molecules is called catenation. Due to catenation compounds of carbons have long chains of carbon, branches chains of carbon and even carbon atoms arranged in rings.

Question 4: What do you understand by a homologous series? Explain giving one example of homologous series. OR Define homologous series of carbon compound. List any two characteristics of a homologous series.Answer 4: A homologous series is a group or family of compounds which contains the same functional group but have different chain lengths. Thus, these have the same chemical properties but different physical properties that vary in a regular manner. Characteristics of a homologous series are: (i) It has a general formula in terms of number of carbon atoms. (ii) It has the same functional group, if any. (iii) The members of a homologous series, i.e., homologous, have similar chemical properties. (iv) Various homologous can be prepared by the general method of preparation for the series. (v) Two successive (adjacent) homologous differ by 1 carbon atom and 2 hydrogen atoms in their molecular formulae. (vi) The member of a homologous series show a gradual change in their physical properties with increase in molecular mass.

Question 5: What will happen if ethanol reacts will ethanoic acid in the presence of an acid? Name the reaction. Write the chemical equation for the reaction.Answer 5: Ethyl alcohol reacts with acetic acid (ethanoic acid) in the presence of a few drops of conc. sulphuring acid to form a sweet smelling substance called ester (ethyl acetate). Such a reaction is called esterification.

Question 6: (a) Distinguish between ethanol and ethanoic acid on the basis of (i) litmus test, (ii) reaction with sodium hydrogen carbonate. (b) Name the oxidising agents used in the conversion of ethanol to ethanoic acid.Answer 6: (a) Ethanol shows no change/reaction with either litmus paper or sodium hydrogen carbon. Ethanoic acid solution in water turns blue litmus red. It reacts with sodium carbonate with effervescence and gives out carbon dioxide gas which turns lime water milky. (b) Alkaline potassium permanganate turns ethanol to acid.

Question 7: Explain saponification.Answer 7: the reaction of an ester to react with an acid or base to give back the alcohol and carboxylic acid is called saponification. This is so-called because this reaction is used in the preparation of soap.

Question 8: Soap does not form lather with hard water. Why? Or Why do soaps not work in hard water? Or Why do soaps from scum instead of lather in hard water?Answer 8: When soap is added to a sample of hard water, calcium and/or magnesium ions present in hard react with soap forming insoluble calcium/magnesium soap which is a sticky and greasy mass and thus no lather is formed.

Question 9: How does soap help to wash the clothes? Or Explain the cleansing action of shops.Answer 9: Dirt is generally absorbed in the clothes as an oily material. It cannot be removed with water because it does not mix well with water. But when a cloth with dirt is soaked in soap solution, the dirt and grease attach themselves to the hydrocarbon component of the soap molecule. The ― COONa part of the soap which is attached to the water molecules pulls the hydrocarbon part along with dirt away from the surface of the cloth, thus washing it clean.